Transformation products and mechanistic pathway of levofloxacin degradation in aqueous solution using advanced oxidation processes in the presence of BiVO₄ and visible light

The degradation of levofloxacin by bismuth vanadate (BiVO₄) catalyst and visible light was carried out in aqueous solution under optimized conditions. The drug degradation was monitored by observing the change in its absorbance value (l 290 nm) using a spectrometer. Levofloxacin degraded by almost 76% in 170 min under optimized conditions and followed the first order kinetics (rate constant was 0.0089 min^–1). LC-MS technique, in addition to tandem mass spectrometry, was used to elucidate the structures of the proposed transformation products/intermediates. Three main initial products were determined after 30 min of reaction (Compound I Fig. 4: (S)-9-fluoro-2,3-dihydro-3-methyl-10-(4-methylpiperazin-1yl)-[1,4]oxazino-[2,3,4-ij]quinolin-7-one, Compound IV Fig. 4: (S)-3,7-dihydro-3-methyl-10-(4-methylpiperazin-1-yl)-7-oxo-2H-[1,4]oxazino-[2,3,4-ij]quinolone-6-carboxylic acid, and Compound X Fig. 5: (S)-3,7-dihydro-9-hydroxy-3-methyl-7-oxo-10-(piperazine-1-yl)-2H-[1,4] oxazino-[2,3,4-ij]quinolone-6-carboxylic acid). Several pathways for the degradation of levofloxacin can be recognized. They involve mechanisms such as demethylation, defluorination, decarboxyl-ation, deamination, and hydroxylation resulting in the production of many different transformation products such as malonic acid, piperazine, acetaldehyde, pyridone, and methylketone.